1. Field of the Invention
This invention relates generally to counting systems and more specifically to a counting system employing fully clocked digital circuits for processing cyclic waveforms to provide display and/or displacement indicative signals suitable for subsequent processing.
2. Brief Description of the Prior Art
Various devices have been proposed heretofore for the purpose of determining the position of a movable element by processing pulse signal outputs of an electro-optical transducer. Examples of such prior devices are illustrated in U.S. Pat. Nos. 2,886,717 and 3,487,399.
Earlier signal processing and counting systems employed RC networks which were time and temperature dependent and did not provide well defined pulse widths. Additionally, these systems were highly susceptible to both internal and external noise which resulted in generally poor reliability.
Further, an adjunct of most counting systems was the provision of an optical numerical readout indicative of the measured displacement of the movable element. Various problems were encountered when the movable element was returned to its reference position due to conventional counting system number display representation of the count. In prior counter-display arrangements, the display decremented in various fashions. For example, in one conventional display circuit the display decremented in the following manner: 2, 1, 0, -1, -2, -3 etc.; another conventional counting arrangement decremented in the following fashion: 3, 2, 1, 0, 9999, 9998, 9997, etc.
In the first instance, true zero actually was the transition edge between a display of 0 on one side and a display of -1 on the other, while in the second instance true zero was the transition edge between a display of 9999 on one side and 0 on the other side. In both of these prior systems, zero was difficult to reconcile by an operator attempting to calibrate the system as a true unambiguous edge between two displays rather than at the 0 display itself. Thus, in prior counting system human understanding and appreciation with respect to calibration and display interpretation was hampered by inherent display-counting system limitations.